川中安岳气田寒武系龙王庙组储层多期自生石英的地球化学演化及其流体历史重建

The Cambrian Longwangmiao Formation is characterized by elderly geological age, deeply bury and long-evolution history in Anyue structure of central Sichuan basin. The reservoir has apparently experienced multiphase's diagenetic fluid charging and modification, resulting in forming multiple minerals filling, such as dolomites, calcites, quartzes and bitumen. Through analysis of digenesis environment and sequences, three phases of authigenic quartzes filling at least were identified. The 87Sr/86Sr, δ13C and δ18O values in dolomites and calcites filling in pores, holes are basically similar with host rocks, suggesting the fluid origination of those carbonate minerals probably came from inner endogenous fluid. While the authigenic quartzes enriching of siliceous fluid were suggested by the 87Sr/86Sr, δ18O values in quartzes and δD isotope information of fluid inclusions. Mutual displacements and replacements existed in process of diagenetic fluid and hydrocarbon accumulation fluid which were hinted by multiphase's authigenic quartzes. Utilizing authigenic quartzes as a geochemical information carrier in reservoir to explore different phases of diagenetic fluid, physical and chemical conditions, crystallization time and so on; comparing to geochemical characteristics of strata water in Anyue structure, to reconstruct evolution history of quartzes precipitation in digagenetic fluid; combining with low temperature thermochronology method to recover geothermal history of the study area, to determine the geological significant of evolution of quartzes fluid. Above scientific problems will be answered by applier on the basis of comprehensive research.

川中安岳构造寒武系龙王庙组时代老、埋藏深、演化历史长；储层经历了多期成岩流体的改造和成藏流体的充注；储层孔洞缝中有多期矿物的充填，白云石、方解石、石英、沥青等；通过成岩环境及成岩序列的研究，认为至少有三期自生石英的充填；孔洞中充填的白云石、方解石的87Sr/86Sr、δ13C和δ18O同位素与龙王庙组围岩基本一致，表明这些碳酸盐岩矿物的流体源为内源异位流体；而石英的87Sr/86Sr、δ18O以及流体包裹体的δD同位素则表明析出自形石英的流体为外来的富硅质流体；孔洞中多期自生石英的沉淀暗示储层中存在成岩流体和成藏流体的相互驱替和置换过程；因此，可以利用储层中的自生石英这一载体探索不同期次成岩流体的流体源、物化环境、结晶时间等地球化学信息，以此与安岳构造现今地层水的地球化学特征相比较，重建析出石英成岩流体的演化历史；结合低温热年代学方法所恢复的研究区热历史，指出石英流体演化历史的地质意义。

本文从岩心和薄片观察入手，利用阴极发光分析、原位微量元素分析、充填物的同位素分析、流体包裹体分析、激光拉曼分析、磷灰石裂变径迹年代学、矿物年代学分析等技术手段，确定了龙王庙组储层矿物的胶结充填序列及所记录的油气成藏历史；探讨了龙王庙组储层中多期自生石英的流体包裹体特征及40Ar-39Ar年代学，重点讨论了第Ⅲ期自生石英的地球化学特征所记录的成岩-成藏流体信息。.可以识别出6个期次的碳酸盐岩矿物和3期自生石英的胶结充填序列，认为龙王庙组存在至少6期油气成藏。从早成岩期到埋藏期，矿物所捕获的流体包裹体的相态从液烃包裹体→气液两相烃类包裹体→气相烃类包裹体演化，反映了龙王庙组经历了古油藏形成、古油藏破坏、再次形成古油藏、油裂解为天然气、古气藏形成和喜山期构造隆升期气藏调整定型的过程。.磷灰石裂变径迹分析表明，安岳构造喜山期的隆升幅度约1865m~2030m，为龙王庙组气藏的调整和定型期，这一成藏事件被晚期充填的第Ⅲ期石英所记录。该期石英的87Sr/86Sr、δ30Si、δD-SMOW、δ18O同位素表明其主要源于含硅质的成岩流体，与深部幔源热液流体的活动无关，龙王庙组油气成藏过程中未见外来破坏性流体的参与，但石英的δ30Si、δ18O同位素与气藏深度的协同变化关系和同位素分馏效应记录了晚期气藏形成的过程中存在气水界面的下移过程。.本文将经历过多期构造演化背景储层的成岩~成藏演化相结合，明确了龙王庙组储层胶结充填序列及所表征的油气成藏历史，厘定了主要成藏期的矿物年代学，确定了油气充注的时间、年代和成藏演化；重点分析了最晚期石英的流体地球化学及所记录的油气成藏和调整的信息，对四川盆地深层古老碳酸盐岩层系的油气勘探有借鉴意义。